Process for the preparation of pentaerythritol



Patented Nov. 1, 1949 PROCESS FOR THE PBEPAR'A-TIONOF PENTAERYTHRITOLJoseph A. Wyler, Allentown, .Pa., assignonto Trojan Powder.-Company, acorporation of New York No Drawing. Application March. 1; 1946,-

Serial No. 651,385.

3 Claims. 1.

This invention relates to the preparationuof pentaerythritol;.particularlyrtoa process :forathe preparationrof pentaerythritol by'thecondensation of acetaldehyde with; formaldehyde 1 of .spe-' cial kindinalkaline medium;

This application isv a -continuation in part of my. application Serial:No: 569,656 filed by 'me on Deeember22,..194s4, now. abandoned; andentitled Process for the preparation of pentaerythritol.

The-principal object of myinvention is to pro-:

quire a period"of.-from-say ten hours-toiseveralv days or even toseveral! months for thereaction to properlycomplete itself: if thetemperature of the reactiomissheldat30 C-..or.less.w In those. processesin: which. thee temperature of; :the reaction is al lowedlto exceed 30-C-athe time of. the reaction is shortened considerably, butcertain sidereactions take placelwhichtare undesirable:

I have discovered that. aqueous solutions of for- I maldehydeof thesamepercentage composition are not identical fromthe standpointof'chemical'reactivity in makingpentaerythritol; Some f thesexsolutions -1 reactmuch. more rapidly than:- others, under identical conditions. The causeofa these differences in reactivity is considered to be dueto' changesaccompanying the distillation of the formaldehyde from aqueous. solutionbefore use, not to difference in chemical composition or purity; but.to. variation: inzzphysical; "relationship such as variations in therotationalxstructure(see.

Chemical Abstracts 28, 3305, article by Dieke and Kistiakowsky);including the valence electrons and possibly the electron angle.

hyde and acetaldehyde are caused to react upon each other in: aqueous*alkalinmmedia, very significant differences in reaction rates areobtained under What appear 'to" be identical conditions. With someformaldehydes it- 'is' not possible to satisfactorily complete thereaction, at C., over a time interval of as much as a week, whereas withother formaldehydes the reaction completes itself within a few hours oreven less.

I have discovered that if there is used, in the Whatever the reason; Ihave discovered that, when formalde reaction mentioned above, aformaldehyde which.

has a specific type of light. transmission, the re-' action uniformlycompletes itself within a matter of minutes or of a few hours. Ihave'discovered that, when a form of formaldee hyde that in a 30% (byweight) aqueous solution:

has a specific light transmission at 25 C. of more than 79% for light of320 millimicron wave length is used in the reaction, a considerablygreater speed of reaction is obtained along with an improvement in theyield 'of 'pentaerythritol. Particularly quick and effectivecondensation is obtained when the formaldehyde used has a transmission.of 80-85% or more for 320 millimicron light. When, on the other hand,the transmission mentioned above is as low as 69%, the formaldehyde isof poor reactivity for the condensation and not dependable in thisreaction.

It is known that formaldehyde in the presence of water undergoeshydration to dihydroxymethane, CI-Iz'(OI-I)z, and that the percentage ofthe formaldehyde so hydrated increases with the proportion of water toformaldehyde. At low temperatures and in dilute solutions the proportionof the total formaldehyde so hydrated'may reach about or more.

Inxmaking the special formaldehyde of low' specific transmission forlight of the wave length 320' millimicron-s (3.200 Angstrom units), thef formaldehyde is distilled from a dilute aqueous solution previous touse in the condensation with acetaldehyde to make pentaerythritol.Preferably-the distillation is from an aqueous solution In'themethod ofmaking this special alcohol of the desired low transmission for light ofstated Wave length,th'e middle cut of the distillation is" used, aforeshot 'of say 10% by weight being rejected and the 'last'30% or 40%or so being left as a residue inthe still. The foreshot and-residue I of'30to 40% may be combined and reworked by the distillation'process orused for other chemical purposesimwhich the special kindof'formalde'hyde' is not a factorin the rate of reaction" or'the yield.-

The weaker the'solution of formaldehyde sub jected to-thisdistillatiomthe greater the proportion'of the formaldehyde distilledthat passes the More specifically,

Example 1 906 parts of water were placed in a suitable vessel providedwith a stirrer and a jacket for regulating the temperature of thereaction mixture. Then 409.6 parts of 29.3% CH2O in water were added andthe mixture stirred. This mixture therefore contained 1196 gms. of waterand 120 gms. of CHzO.

The formaldehyde used when tested in the form of a 30% formaldehdye inwater solution, had a specific transmission at 25 C. of 81% for 320millimicron light when using the standard Beckmann spectrophotometer andthe 1 cm. quartz cells.

To this mixture, 44 parts of 99.5% acetaldehyde were added in a steadystream over a period of two hours while simultaneously adding a limeslurry consisting of 58 parts of hydrated lime and q Example 2 In asimilar experiment, except that the for-.

maldehyde used had a specific transmission of 85% for 320 millimicronlight, the reaction was completed in about 4 hours to an endpoint ofCHzO and the yield was over 88% of theory.

Although in the examples, a temperature of reaction of C. is given, I donot confine myself to this specific temperature. I may use tempera:tures as high as 50 C. in which case the acetaldehyde is added morerapidly than mentioned in the example given above or I mayusetemperatures as low as 5 C. in which case the rate of addition of theacetaldehyde is usually slowed down. When temperatures as high as to C.are used for the reaction, this highly reactive formaldehyde not onlyperforms the function of completing the condensation in less than onehour but also serves to prevent the formation of colored syrups whichcause difficulties in subsequent purification operations.

Also, in the examples, the acetaldehyde is added to the formaldehyde,but this is not absolutely necessary. It is, however, the preferredmethod. The aldehydes may be mixed previous to the addition of alkali orthey may both be added simultaneously. If they are mixed together beforeadding the alkali there is a tendency to produce more dipentaerythritol,as an impurity in the pentaerythritol, than when the condensations arerun in accordance with the examples given.

The preferred proportion of formaldehyde to acetaldehyde is fourmolecules of CHzO to one molecule of CHsCHO but other proportions asfrom 3 to 1 to 4.5 to 1 may be used.

The alkali used may be any water-soluble, fixed alkali such as Ca(OH)2,Ba(OH) 2, NaOI-I, KOH,

mixtures of these, etc.; and the proportions used and the manner ofaddition of the alkali may be varied considerably provided there isalways an excess of alkali present throughout the condensation.

The concentrations of reactants may also be varied over a wide range,but in general the preferred concentration of aldehydes is such as tocontain at least 3% CH2O but not to exceed 20% CHzO at the beginning ofthe condensation.

For purposes of this invention the term formaldehyde is intended tocover the compound CHzO in either pure or commercial form. Specifictransmission means the percentage of the light, of 320 millimicronwave-length, entering an aqueous formaldehyde solution of 30% CH2O byweight, at 25 C., that passes through a layer of the solution of 1 cm.thickness, all measurements being made with the standard Beckmannspectrophotometer and with the use of quartz cells.

The final reaction mixture contains the pentaerythritol in solution andmay be processed in accordance with any of the well known methods now inuse for the separation of the pentaerythritol in pure or commercialcondition.

It will be understood also that it is intended to cover all changes andmodifications of the example of the invention herein chosen for thepurpose of illustration which do not constitute departures from thespirit and scope of the invention.

I claim:

1. In making pentaerythritol the method which comprises distillingformaldehyde from an aqueous solution thereof, this distillation givinga distilled formaldehyde of high specific transmission for light of wavelength 320 millimicrons, forming a mixture of the distilledformaldehyde, at a time when the specific transmission for light ofthesaid wave length is not less than 79%, with acetaldehyde and anaqueous solution of a fixed alkali and maintaining the resulting mixtureat a temperature not above 50 C. until the reaction between theformaldehyde and acetaldehyde to give pentaerythritol is substantiallycomplete.

2. The method described in claim 1, the alkali used being calciumhydroxide.

3. The method described in claim 1, the proportions of the two aldehydesbeing 44 parts by weight of acetaldehyde to about parts of actualformaldehyde, about 1196 parts of water and 58 parts of calciumhydroxide, and the temperature at which the mixture is maintained beingabout 30 C.

JOSEPH A. WYLER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,004,010 Nanjoks June 4, 19352,381,855 Spence et a1 Aug. 7, 1945 OTHER REFERENCES Gilman, OrganicSyntheses, Collective v01. 1 2nd ed.) pp. 425-427.

